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                3.93.0
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  <section id="help">
<span id="library-help"></span><h1><code class="docutils literal notranslate"><span class="pre">help</span></code><a class="headerlink" href="#help" title="Link to this heading"></a></h1>
<p>This tool provides basic online help for Logtalk features and libraries
when running in most operating-systems. For help on the Logtalk compiler
error and warning messages, see the <code class="docutils literal notranslate"><span class="pre">tutor</span></code> tool.</p>
<section id="requirements">
<h2>Requirements<a class="headerlink" href="#requirements" title="Link to this heading"></a></h2>
<p>On Windows, the <code class="docutils literal notranslate"><span class="pre">start</span></code> command must be available. On Linux, the
<code class="docutils literal notranslate"><span class="pre">xdg-open</span></code> command must be available. On macOS, the command <code class="docutils literal notranslate"><span class="pre">open</span></code>
is used.</p>
<p>Experimental features for browsing the Handbook and APIs documentation
at the top-level require Texinfo to be installed. See the
<code class="docutils literal notranslate"><span class="pre">tools/NOTES.md</span></code> file for per operating-system installation
instructions.</p>
</section>
<section id="api-documentation">
<h2>API documentation<a class="headerlink" href="#api-documentation" title="Link to this heading"></a></h2>
<p>This tool API documentation is available at:</p>
<p><a class="reference external" href="../../apis/library_index.html#help">../../apis/library_index.html#help</a></p>
<p>For sample queries, please see the <code class="docutils literal notranslate"><span class="pre">SCRIPT.txt</span></code> file in the tool
directory.</p>
</section>
<section id="loading">
<h2>Loading<a class="headerlink" href="#loading" title="Link to this heading"></a></h2>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(help(loader)).
</pre></div>
</div>
</section>
<section id="testing">
<h2>Testing<a class="headerlink" href="#testing" title="Link to this heading"></a></h2>
<p>To test this tool, load the <code class="docutils literal notranslate"><span class="pre">tester.lgt</span></code> file:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(help(tester)).
</pre></div>
</div>
</section>
<section id="supported-operating-systems">
<h2>Supported operating-systems<a class="headerlink" href="#supported-operating-systems" title="Link to this heading"></a></h2>
<p>Currently, support is limited to Linux, macOS, and Windows.</p>
<p>This tool relies on the library portable operating-system access
abstraction.</p>
</section>
<section id="usage">
<h2>Usage<a class="headerlink" href="#usage" title="Link to this heading"></a></h2>
<p>After loading the tool, use the query <code class="docutils literal notranslate"><span class="pre">help::help</span></code> to get started.</p>
</section>
<section id="experimental-features">
<h2>Experimental features<a class="headerlink" href="#experimental-features" title="Link to this heading"></a></h2>
<p>On POSIX systems, when using Ciao Prolog, ECLiPSe, GNU Prolog (1.5.1 or
later version), XVM, SICStus Prolog, SWI-Prolog, Trealla Prolog, or XSB
as the backend, <code class="docutils literal notranslate"><span class="pre">apis/1</span></code> and <code class="docutils literal notranslate"><span class="pre">handbook/0-1</span></code> predicates are made
available. These predicates open inline at the top-level interpreter the
Texinfo versions of the Handbook and the APIs documentation. The
optional argument is a starting node, which can be an atom, a predicate
indicator, or a non-terminal indicator. When there are several nodes for
the same argument (e.g., multiple implementations of the <code class="docutils literal notranslate"><span class="pre">member/2</span></code>
predicate), one of them will be displayed. Some examples:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> help<span class="o">::</span>handbook.

| <span class="o">?-</span> help<span class="o">::</span>handbook(base64).

| <span class="o">?-</span> help<span class="o">::</span>handbook(logtalk_load<span class="o">/</span><span class="m">2</span>).

| <span class="o">?-</span> help<span class="o">::</span>apis.

| <span class="o">?-</span> help<span class="o">::</span>apis(check<span class="o">/</span><span class="m">2</span>).

| <span class="o">?-</span> help<span class="o">::</span>apis(message_tokens<span class="o">//</span><span class="m">2</span>).
</pre></div>
</div>
<p>Although less useful, you can also browse the <code class="docutils literal notranslate"><span class="pre">man</span></code> pages of Logtalk
scripts. For example:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> help<span class="o">::</span>man(logtalk_tester).
</pre></div>
</div>
<p>When you finish consulting the documentation and quit the <code class="docutils literal notranslate"><span class="pre">info</span></code>
process, you will be back to the top-level prompt (if you find that the
top-level have scrolled from its last position, try to set your terminal
terminfo to <code class="docutils literal notranslate"><span class="pre">xterm-256colour</span></code>).</p>
<p>If you’re running Logtalk from a git clone of its repo, you will need to
run the <code class="docutils literal notranslate"><span class="pre">docs/apis/sources/build.sh</span></code> or
<code class="docutils literal notranslate"><span class="pre">docs/apis/sources/build.ps1</span></code> scripts to generate the APIs
documentation <code class="docutils literal notranslate"><span class="pre">.info</span></code> file and also run the
<code class="docutils literal notranslate"><span class="pre">docs/handbook/sources/build.sh</span></code> or
<code class="docutils literal notranslate"><span class="pre">docs/handbook/sources/build.ps1</span></code> scripts to generate the Handbook
<code class="docutils literal notranslate"><span class="pre">.info</span></code> file. Alternatively, you can download the <code class="docutils literal notranslate"><span class="pre">.info</span></code> files for
the latest stable release from the Logtalk website and save them to the
<code class="docutils literal notranslate"><span class="pre">docs</span></code> and <code class="docutils literal notranslate"><span class="pre">manuals</span></code> directories.</p>
<p>The required <code class="docutils literal notranslate"><span class="pre">info</span></code> command is provided by the third-party <code class="docutils literal notranslate"><span class="pre">texinfo</span></code>
package (tested with version 6.8). On macOS, this package can be
installed with either MacPorts:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span><span class="err">$</span> sudo port install texinfo
</pre></div>
</div>
<p>Or using Homebrew:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span><span class="err">$</span> brew install texinfo
</pre></div>
</div>
<p>On Linux systems, use the distribution’s own package manager to install
the <code class="docutils literal notranslate"><span class="pre">texinfo</span></code> package. For example, in Ubuntu systems:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span><span class="err">$</span> sudo apt install info
</pre></div>
</div>
</section>
<section id="known-issues">
<h2>Known issues<a class="headerlink" href="#known-issues" title="Link to this heading"></a></h2>
<p>The open commands used to open documentation URLs drops the fragment
part, thus preventing navigation to the specified position on the
documentation page.</p>
<p>When browsing the Texinfo versions of the Handbook and the APIs
documentation generated with a recent version of Sphinx and using a
recent version of Texinfo, the Texinfo search feature often displays the
previous nodes of the searched nodes.</p>
<p>ECLiPSe defines a <code class="docutils literal notranslate"><span class="pre">help</span></code> prefix operator that forces wrapping this
atom between parentheses when sending messages to the tool. E.g. use
<code class="docutils literal notranslate"><span class="pre">(help)::help</span></code> instead of <code class="docutils literal notranslate"><span class="pre">help::help</span></code>.</p>
</section>
</section>


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